Body implantable conductor



April 5, 1966 w. H. WESBEY ETAL 3,244,174

BODY IMPLANTABLE CONDUCTOR Filed Jan. 51, 1964 INVENTORS WILLIAM H.WESBEY WILLIAM D. SHADDUCK BY MM- W ATTORNEY United States Patent3,244,174 BODY IMPLANTABLE CONDUCTOR William H. Wesbey, West Allis, andWilliam D. Shadduck, Hales Corners, Wis, assignors to General ElectricCompany, a corporation of New York Filedlan. 31, 1964, Ser. No. 341,525l Claim. (Cl. 128-418) This invention pertains to a conductor that isintended tor implantation in a living body for the purpose of deliveringelectric energy from an implanted source to an organ :that is to bestimulated thereby. An illustrative use of the invention is with acardiac pacemaker constituting an implanted electric pulse source thatdelivers energy to the human heart so that it may be stimulated to beatat essentially a normal rate.

Experience has shown that one of the most frequently encounteredproblems with cardiac stimulators has been breakage of the leads betweenthe source and heart. This is to be expected in view of the fact thatthe conductors of the leads must be very fine and flexible and yetdurable enough to withstand thousands of flexures per day due toexpansion and contraction of the heart. It has been diflicult to findlead insulating materials that have the properties of being bodycompatible and yet flexible and small enough to avoid interference withnormal body iunctiqns. Synthetic plastic. coverings that were usedformerly often cracked and caused a sharp flexure of the wireconductor,causing it to fatigue and break shortly thereafter. The presentinvention is concerned with a conductor lead and conductor lead assemblythat avoids this disadvantage.

:It is the general object of the present invention to provide a bodyimplantable conductor that is small in crosssection, that has goodinsulating properties, that is easily used by the surgeon, and that isdurable.

A more specific object of the present invention is to provide aconductive lead that comprises a flexible stranded wire cable on whichthere are insulating layers of silicone rubber, a Dacron fabricimpregnated with silicone rubber and another layer of silicone rubber.

Another object of this invention is to provide an implantable conductorassembly that is made up as a twin lead.

Another object is to provide new means for anchoring the ends of theconductor assembly to the organ that is to be stimulated .or energizedfrom the electrical source.

The achievement of these and other more specific objects will appearfrom time to time throughout the course of the ensuing specification.

A more detailed explanation of the invention will now be set forth inreference to the drawings in which:

FIGURE 1 shows the outline of a human heart to which an implantedcardiac pacemaker is connected by means of the new lead assembly;

FIGURE 2 is a side View of the new body implantable lead;

FIGURE 3 is across-section of the lead shown in FIG- URE 2 taken on theline 2-2 of the latter;

"FIGURE 4 is a plan view of the lead and means for terminating andconnecting the same to a body organ;

FIGURE 5 is a modified side view of the assembly shown in FIGURE 4;

FIGURE 6 is a plan view of a suture pad; and

FIGURE 7 is an alternative form of lead termination and is comparablewith that employed in the example of FIGURE 1.

In FIGURE 1 use of the new lead assembly 10 is illustrated as connectingan implantable electronic pacemaker 11 with a human heart 12. Thepacemaker 11 may be placed by suitable surgical technics in the patientsabdominal muscular wall a little below the umbilicus or 3,244,174Patented Apr. 5, 19.66

belt line, for instance. The pacemaker is a known type of solid statepulse power source that is encapsulated in body compatible material andis usually about two inches square and under one inch thick. It produceselectric pulses that are generally under four volts at a repetition rateof 70 pulses per minute, this being the normally desired rate of heartbeat.

The lead 10 is usually run from pacemaker 11 t0 he heart through anintercostalspace where it is admitted to the thoracic cavity. Terminalconnection of lead 10 to the heart is made to the myocardium layer aftera suitable incision has been made in the sheathing pericardium to permitexposure of the former. It may be assumed that one is viewing themyocardium in FIGURE 1 and that the pericardium has been omitted.

The insulated ends 24 of the lead lie .on the myocardium layer and oneinsulated portion 24A lies below the layer as indicated by dashed lines.This concealed excursion 24A may be around 1.5 centimeters in length. Abared insulated stranded conductor 20 is brought out in an exposed loopand then permitted to re-enter and be con sealed for another 1.5centimeter distance, approximately, whereupon it terminates in astainless steel ferrule 16. A suture loop 17 is then brough through the.myocardium and around the insulated portion 24 and the bare wire nextto ferrule 16 to efiect an anchorage. Electric current is transferred tothe heart by the concealed bare conductor wire 20 contacting hearttissue of the myocardium.

The above remarks are not intended as a proposal for a surgical technicbut they are made for roughly illustrating an application of the newleads and to serve as a basis for further discussion.

The two most crucial regions of lead 10, insofar as breakage isconcerned, lie immediately next to the pacemaker power supply 11 andnext to the region where the individual insulated end portions 24 of theleads are admitted to the heart tissue. In the first case, normal bodymuscular movements flex and stress the leads. The expansive andcontractile movements of the heart, of course, stress and flex theterminal ends of the leads more than 100,000 times per day. When this ismultiplied by the number of days in a year, one may readily realize thata rigorous performance of the leads is required if replacement at undulyshort intervals is to be avoided. I

The new lead may be made up as either a pair of individual insulatedleads that run from the power source to the organ being stimulated, orthey may be bound together as a twin lead assembly. In either case, theleads are made in a new way that is illustrated in FIG- URE 2. Here theactual current carrying portion comprises a stainless steel strandedcable 20 which is usually composed of No. 316 stainless steel which hasa total diameter of 0.015 inch and is made up of 49 individual wires inseven bundles. Each wire is less than two-thousandths of an inch indiameter. Cables such as 20 have been used with insulating coatingsother than the new one which will now be described.

In accordance with the invention, stranded stainless steel conductor 20is coated with a layer of medical grade silicone rubber 21. This layermay penetrate between the strands of cable 20 but the material is notintimately bonded with the strands as that term is ordinarilyunderstood. A suitable silicone material for layer 21 that is known byDow-Corning Corporations trademark Silastic. Immediately on top ofsilicone rubber layer 21 is deposited a mesh material 22. The meshmaterial may be a braid of ten picks per inch and constitute a singlewrap. The mesh is preferably a polyester fiber such as that sold underthe Du Pont Company trademark Dacron. There is then concentricallyextrudedover mesh layer 22 another external layer of Silastic 24 whichgoes through ordinarily have mesh in it. at the same time and integralwith the extruded layer 24 'that penetrates the mesh 22 which isordinarily only the mesh and joins with layer 21. The layers 24, 22 and21 and the stranded cable 20 constitute a round crosssection insulatedconductor that is useable by itself as a means for interconnecting apower source and an organ in a living body. In a practical case, theoutside circular part of the lead that is bounded by Silastic layer 24may have a diameter of about V of an inch.

In FIGURE 3 an extension of this basic construction is evident. In thisfigure a twin conductor lead assembly is formed by joining two of theconductors above described by a web 25 of silicone rubber which does notThe web 25 may be formed wrapped around the individual conductors 20.The straight part of the web 25 between the circumferences of theadjacent insulated conductors may have a length and thickness of 0.04inch. The overall width of the twin lead as viewed in FIGURE 3 is 0.16inch in a practical case. The twin conductor of FIGURE 3 is also usefulfor connecting other types of electric stimulators to body organsbesides the cardiac pacemaker application discussed above.

A new means for utilizing and terminating and connecting the abovedescribed lead assembly to an organ is shown in FIGURES 4 and 5. Herethe lead assembly 10 is provided with a suture pad 26 that facilitatesconnection with the heart, for example. Suture pad 26 is shown in detailin FIGURE 6 and is seen to comprise a fiat silicone rubber rectangularpad that has a Dacron mesh 40 similar to that described above imbeddedin it to improve toughness. The pad has a pair of spaced slits 27 and27' that are separated by an imperforate region 28. Suture V pad 26 maybe slid over lead assembly 10 by passing the end of the lead under theleft end of suture pad 26 as viewed in FIGURE 6 whereupon the lead maybe passed in a serpentine path upwardly through slit 27 and overintervening portion 28 and then down through slit 27 so that the outsideinsulating layer terminates under the suture pad 26 in a manner that maybe seen best in FIGURE 5. Pad 26 may also have any desired number ofholes 34 to facilitate suturing it to tissue. It is desirable to applyan adhesive such as Silastic medical adhesive in the vicinity of theslits 27 so that the lead cannot slip with respect to the pad. Forinstance, a few droplets 41 of adhesive may be applied as shown inFIGURE 4.

One may see particularly well in FIGURE that the bare stranded conductorsection 20 is formed into an eye 29 which is seized by a ferrule 30which may be stainless steel. Before installation, eye 29 is engaged bya suture 31 or other suitable material that is in turn swedged to asurgical needle 32. Needle 32 is cut off of suture 31 after installationwhich Will now be described.

Making an electrical connection between the lead and tissue may bereadily understood by referring to FIGURE '5 where it is seen that thelead rests on the myocardium layer 12 of the heart, which is shown inoutline, with suture pad 26 on top. Before the assembly is pulled down,the needles 32 are passed through the heart tissue and back throughsuture pad 26 until the eye- 29 is brought up tightly against the bottomof the pad. A knot 33 is then made so as to' prevent eye 29 from drawingaway from the suture pad. In due course, it is expected that tissuefibrosis will occur in the vicinity of eye 29 and ferrule 30 to serve asa more secure anchor for the conductor. However, there remains aconstant impedance current interchange surface between the tissue andthe bared portion 20 of the conductor. Both eyes 29 are secured in themanner just described and suture pad 26 is further secured byappropriately suturing through small holes 34 in the latter, forinstance.

An advantage of using suture pad 26 as a supporting and fastening meansfor lead is that it serves as an insulator between the my c rdi m an peicardium l y rs of the heart. Hence, current that is conducted from bareconductor 20 to the "myocardium does not find a dire'ct path into thepericardium. The benefit of this is that the phrenic nerve is notstimulated inadvertently by the elec trical energy that is beingsupplied to the heart. The phenic nerve passes from the brain along thepericardium layer, not shown, and to the diaphragm. If it is stimulated,the patient may hiccup at the pulse rate and further surgical proceduresmay be necessary.

Another form of lead assembly which is constructed according to theconcepts described primarily in conned tion with FIGURES 2 and 3, isseen in FIGURE 7. It this construction that is shown applied to theheart in FIGURE 1 except that surgical needles 32 and the continuousstainless steel conductive suture 20 are still intact. In FIGURE 7, thetwin conductor assembly terminates in the region of broken line 37 afterwhich conductors 24 that are insulated according to the inventioncontinue separately. Along line 37, where web 25 is discontinued, thereis provided a loop of mesh 38 that is impregnated with silicone rubber.The purpose of the mesh is to act as a re-enforcement for preventing thespreading and tearing away of the twin conductors 13. It will beobserved that conductors 24 have their insulating layers terminated in aconical or pointed configuration which is obtained by installing atapered plug 39 of silicone rubber on the conductor cables before theferrule 16 and needles 32 are fastened. This permits the individualconductors to be drawn through tissue with less resistance and withoutundue trauma.

It should be understood that the new lead may be used as individual orseparated conductors or in its twin con-r figuration. In some cases itis preferred to run for a distance with separated conductors and thencontinue unin terruptedly with the twin configuration. For example, inFIGURE 1, the leads are separate where they emerge from pacemaker 11.This facilitates introducing slack in the line and it has beendiscovered that in the abdominal muscle site where the pacemaker isimplanted that muscular action constrains the twin configuration to bendin a manner that may increase the likelihood of breakage as comparedwith the use of separated leads. This slack is necessary for allowingthe source and organ to change distance due to normal body movements andbody growth. On the other hand, the twin configuration has been found tooffer greatest surgical convenience and ruggedness for the remainder ofthe lead to the organ. In some instances, a suture pad such as 26 may beplaced on the lead and sutured to the tissue intermediate the twin andseparated parts to isolate one stress condition from another.

In summary, a body implantable lead has been described that insulates astranded cable with alternate layers of silicone rubber. Dacron meshthat is impregnated with silicone rubber, and an extended layer ofsilicone rubber over it. The invention includes single conductors thatare insulated in this manner and in the alternative and V as a furtherextension, contemplates joining such con: ductors in a twinconfiguration by a web of flexible insulating material. Further, a newsuture pad fastenin means has been described.

Although specific embodiments of the invention have been described,these are to be considered illustrative. rather than limiting, for theinvention may be variously embodied and is to be limited only by thescope of the claim which follows,

It is claimed: A body implantable lead assembly comprising: (a) at leasttwo spaced apart substantially parallel flexible wire conductors, (b) afirst coating of pliable silicone rubber surrounding each of saidconductors, (c) a polyester fiber mesh that surrounds each of, Saidifirst coatings individ ally,

(d) a second coating of pliable silicone rubber that penetrates the meshlayers individually and which coating is continuous to form a Web thatjoins the conductors together along at least part of their length,

(e) a suture pad of polyester fiber mesh that is impregnated vvithsilicone rubber,

(f) said pad having spaced apart slits therein for passing said leadconsecutively through them,

(g) and silicone medical adhesive applied in the vicinity of the slitsto join the suture pad with the second coating,

(11) said adhesive joining said lead and pad in the region between theslits where the lead extends through the pad.

References Cited by the Examiner UNITED STATES PATENTS 1,729,160 9/1929Engle 1741l3 3,057,356 10/1962 Greatbatch.

FOREIGN PATENTS 93 8,976 2/ 1956 Germany. 743,396 1/1956 Great Britain.830,644 3/ 1960 Great Britain.

RiCHARD A. GAUDET, Primary Examiner.

W. E. KAMM, Assitant Examiner.

